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Sea surface temperature (SST) in European seas is increasing more rapidly than in the global oceans. The rate of increase is higher in the northern European seas and lower in the Mediterranean Sea. The rate of increase in sea surface temperature in all European seas during the past 25 years has been about 10 times faster than the average rate of increase during more than the past century. The rate of increase observed in the past 25 years is the largest ever measured in any previous 25 year period.

Key messages

Sea surface temperature (SST) in European seas is increasing more rapidly than in the global oceans. The rate of increase is higher in the northern European seas and lower in the Mediterranean Sea.

The rate of increase in sea surface temperature in all European seas during the past 25 years has been about 10 times faster than the average rate of increase during more than the past century.

The rate of increase observed in the past 25 years is the largest ever measured in any previous 25 year period.

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Sea surface temperature anomaly for period 1870-2006

Note:Data (oC) show the difference between annual average temperatures and the period 1982-2006 mean in different European seas

Coppini, G. and Pinardi, N., 2007. Compiled for EEA by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) based on datasets made available by the Hadley Center HADISST1: http://hadobs.metoffice.com/hadisst/data/ download.html.

Past trends

The SST changes in the European regional seas are stronger than in the global oceans (Table 1). The strongest trend in the last 25 years is in the Baltic Sea and the North Sea, while the rates are lower in the Black Sea and Mediterranean Sea. The regional seas experienced warming rates that are up to six times larger than those in the global oceans in the past 25 years. These changes have not been observed in any other 25-year period since systematic observations started more than a century ago (Figure 1). The spatial distribution of trend over the European seas is shown in Figure 2. It shows that the positive temperature trend is more pronounced in the North Sea, Baltic Sea, the area south of the Denmark Strait, the eastern part of the Mediterranean, and the Black Sea. Absolute maxima are located in the North Atlantic around 50oN, in the North Sea and Baltic Sea, with values over 0.06-0.07 oC/year. Negative trends are detected in the Greenland Sea. Here, the estimates also depend on the extent of the ice.

Projections

IPCC (2007a) reports global-scale SST patterns for the SRES-A1B scenario for 2011-2030, 2046-2065, and 2080-2099. In these scenarios, ocean warming evolves more slowly than the warming of the atmosphere. Initially ocean warming will be greatest in the upper 100 m of the ocean (in the surface mixed layer), but later in the 21st-century temperatures will also increase in the deep ocean (IPCC, 2007a; Watterson, 2003; Stouffer, 2004). The scenario projects ocean warming to be relatively large in the Arctic and along the equator in the eastern Pacific, with less warming over the North Atlantic and in the Southern Ocean (e.g. Xu et al., 2005). Enhanced oceanic warming along the equator is also evident, and can be associated with oceanic heat flux changes (Watterson, 2003) and temperature changes in the atmosphere (Liu et al., 2005). It is not possible to project changes in SST for the different geographic regions across Europe because the spatial resolution of the coupled ocean-climate models is not high enough to evaluate trends on the scale of individual European regional seas.

Table 1 Summary of sea surface temperature changes in the global ocean and the four

Units

Rationale

Justification for indicator selection

RelevanceSea surface temperature (SST) is closely linked to one of the strongest drivers of climate in western Europe: the ocean circulation known as the Atlantic Meridional Overturning Circulation (MOC). This circulation (also known as the great conveyor belt) carries warm upper waters north in the Gulf Stream and returns cold deep waters south. It is widely accepted that the MOC is an important driver of low frequency variations in sea surface temperature on the time scale of several decades (Griffies et al., 1997). It is also widely accepted that the NAO index (a proxy of atmospheric circulation variability) plays a key role in forcing variations in MOC as well as the northward extent of the Gulf Stream (Frankignoul and Kestenare, 2005; De Coetlogon et al., 2006). At present, changes in sea surface temperatures of the global ocean and the regional seas of Europe are consistent with the changes in atmospheric temperature (Levitus et al., 2000; Rayner et al., 2006).The sensitivity of the MOC to greenhouse warming, however, remains a subject of much scientific debate. Observations indicate that there has indeed been a freshening of the North Atlantic since 1965 due to increased freshwater inputs from rivers, precipitation and melting glaciers (Curry and Mauritzen, 2005), and thus possibly a weakening of the Atlantic MOC. The freshening calculated by these authors occurred mainly before 1970 and does not yet appear to have substantially altered the MOC and its northward heat transport. Uncertainties regarding the rates of future climate warming and glacial melting limit the predictability of the impact on ocean circulation, but do not exclude the possibility of a weakening of the MOC. Recent observations, have, however, shown that the variability of the MOC is large. The yearlong average MOC is 18.7 ± 5.6 Sverdrup (Note: Sverdrup = 106 m3s-1) but with large variability ranging from 4.4 to 35.3 Sverdrup (Cunningham et al., 2007). A recent study has shown that the variability of the MOC may be predictable on decadal time scales, and the study predicts that North Atlantic and European sea surface temperatures will fall slightly in the next decade as natural climate variability off-sets the projected anthropogenic warming (Keenlyside et al., 2008). The plausibility of the Keenlyside et al., 2008 projections are, however, also subject to intense debate in the scientific community (see e.g. http://www.realclimate.org).One of the most visible ramifications of increased temperature of the ocean is the reduced area of sea ice coverage in the Arctic polar region and there is an accumulating body of evidence suggesting that many marine ecosystems are responding both physically and biologically to changes in regional climate caused predominantly by the warming of air and SST, as shown in the following sections.

Scientific references

No rationale references
available

Policy context and targets

Context description

In April 2009 the European Commission presented a White Paper on the framework for adaptation policies and measures to reduce the European Union's vulnerability to the impacts of climate change. The aim is to increase the resilience to climate change of health, property and the productive functions of land, inter alia by improving the management of water resources and ecosystems. More knowledge is needed on climate impact and vulnerability but a considerable amount of information and research already exists which can be shared better through a proposed Clearing House Mechanism. The White Paper stresses the need to mainstream adaptation into existing and new EU policies. A number of Member States have already taken action and several have prepared national adaptation plans. The EU is also developing actions to enhance and finance adaptation in developing countries as part of a new post-2012 global climate agreement expected in Copenhagen (Dec. 2009). For more information see: http://ec.europa.eu/environment/climat/adaptation/index_en.htm